Medical diagnostics, but also other fields, encounter the problem of needing to detect specific analytes quickly and reliably, sometimes even a number times in a day. By way of example, diabetics often have to monitor their blood glucose levels up to seven times a day. So as not to restrict the daily routine of the user more than necessary as a result of these frequent checks, hand-held instruments were developed that also allow monitoring the blood glucose levels during free time or at work. Here, a lancet punctures skin of the user, for example on a finger tip or on an ear lobe. This generates a blood sample or a sample of interstitial fluid. This sample is then examined in respect of its blood sugar level and/or the level of another type of analyte by means of a test instrument and a test element, for example an electrochemical and/or optical test element.
In addition to individual strip test instruments, tape instruments have also been disclosed in the meantime; here, test elements are provided in the form of test tapes. These test tapes contain a plurality of test fields with corresponding test chemicals, the properties of which change in the case of contact with the analyte to be detected. In addition to analytic test instruments with analysis tapes in the form of test tapes, analytic test instruments with analysis tapes that contain a plurality of lancets have also been disclosed in the meantime. Here, lancets are successively provided on a carrier tape in an application position of the test instrument and can be used for generating the sample. By way of example, the analysis tape can be provided by a supply reel, with used analytic aid, e.g. test fields and/or lancet elements, are wound up on a take-up reel after use.
WO 2008/138443 A1 shows a pricking system with a carrier tape that carries a plurality of lancets. Furthermore, provision is made for a conveyor apparatus for successively bringing the lancets into an application position by moving the carrier band in a conveying direction. Moreover, provision is made for an actuation device for driving the conveyor apparatus. The pricking system furthermore comprises a detachable lock that blocks further transport of the carrier tape as soon as a lancet has reached the usage position.
WO 2009/037341 A1 has disclosed a sample extraction system for extracting a liquid sample, which system has at least one analytic aid. The sample extraction system has a coupling element for coupling onto the analytic aid and at least one drive unit for driving a movement of the coupling element from a rest position into an extended position. The drive unit comprises an energy transducer that is embodied to produce a rotational movement with different directions of rotation. The drive unit furthermore has a coupling device with at least one rotational direction-sensitive element that is designed to couple the energy transducer to a first system function in the case of a first rotational direction and to couple said energy transducer to a second system function that differs from the first system function in the case of a second rotational direction that differs from the first rotational direction.
For different reasons, both WO 2008/138443 A1 and WO 2009/037341 A1 disclose so-called friction clutches in various embodiments, particularly in a drive for the analysis tapes. By way of example, these friction couplings can comprise spiral-spring elements. Here, all the friction clutches disclosed in these documents are based on the fact that one or more resilient, elastic or spring-mounted arms or other types of elastic pick-up elements such as spiral springs slip in a punctiform fashion on a friction surface of a counterelement and interact with projections on this counterelement. The pick-up elements catch on these projections and entrain these as long as a maximum torque is not exceeded. This maximum torque is specified by the elasticity and shape of the pick-up elements and projections because as the torque increases the pick-up elements are pressed away from the friction surface of the counterelement and/or the projections and slip over these projections above the maximum torque. However, this means that the maximum torque or limit torque is fixedly prescribed by the geometry of the projections and the pick-up elements, and by the material properties and bending moments of the pick-up elements, and, in particular, cannot be adjusted. Furthermore, significant amounts of noise are generated when the pick-up elements slip over the projections. Such spring-based friction clutches are often also referred to as free wheels or are embodied as free wheels.
By way of example, the pricking system configuration with the conveyor apparatus disclosed in WO 2009/037341 A1 generally requires at least one friction clutch for three reasons. Thus, a friction clutch may be provided to compensate for tolerances that emerge from the production of the analysis tapes. Furthermore, the friction clutch is provided to compensate for the variation in the take-up reel diameter, which increases during continued cycling. Thirdly, the friction clutch is designed to prevent mechanical damage to the tape because, once the lancet has reached the usage position, unintentional further transport could lead to the lancet becoming detached or the analysis tape becoming deformed. The friction clutch ensures that the drive is released by slipping through before there is such mechanical damage to the tape, and so mechanical overstress is avoided. By way of example, spiral springs can be used for this.
There is a change in the roll thickness on both a supply reel and a take-up reel as a result of e.g. winding up the tape, particularly when conveying lancet tapes but also in the case of other types of analysis tapes, and so different travel paths of the tape have to be overcome whilst applying the same force per continued cycle. If the travel path of the roll is very short, the excessive force must be dissipated. By way of example, this is achieved by the friction clutch. Here, provision can for example be made for metal springs that are constantly under a certain amount of pressure, resulting in constant tensile force acting on the tape.
However, the systems known from the prior art have various disadvantages or technical challenges, particularly for the use of lancet tapes. Thus, for example, as set out above, WO 2008/138443 A1 provides a detachable lock, for example in the form of a gripper, that both serves to stop the tape if the lancet is transported past it and also is used for the pricking procedure. However, in the friction clutches known from the prior art, a permanent force acts on the analysis tape, for example as a result of the pretensioned spiral springs. These spiral springs, e.g. metal springs, are always under a specific pressure, as a result of which a constant tensile force acts on the tape. As a result, the user must also apply more force to operate the system, which may be disadvantageous; this is the case in e.g. the system described in WO 2008/138443 A1. A further disadvantage relates to the acoustic component since minimum dead travel must be implemented; this can generate uncomfortable background noise. This is based on the functionality of a spring friction clutch, which contracts and slips over obstacles. Noise is generated every time an obstacle is overcome. However, in order to achieve as little dead travel as possible, a plurality of these obstacles are required, distributed over 360°. A further disadvantage consists of the fact that a difficulty in known spiral-spring systems lies in providing springs whose physical volume can be accommodated in the core of a reel; this may, in certain circumstances, lead to an increase in the overall size of the system as a result of this component.
Hence, in conclusion, known spring friction clutches for test instruments are disadvantageous in having a dead travel, which in many cases does not allow precise gripping of the friction clutch. Furthermore, significant amounts of noise are generated as a result of the punctiform interaction between the pick-up elements and projections; this noise can in particular lead to the user experiencing insecurity and can significantly reduce user comfort. Furthermore, the maximum torques of the friction clutches are generally fixedly prescribed by geometries and material properties of the pick-up elements and/or projections and cannot be adjusted.
In principle, friction clutches are known from heavy mechanical engineering. Thus, for example, DE 10315808 A1 describes a friction clutch with a sleeve-shaped hub for holding a drive element and a clamping part, situated at the end, with a slit extending in the region of a radial central plane and with a clamping screw bridging the slit and acting in the circumferential direction of the clamping part. A drive element is arranged between two friction linings, which are in turn arranged axially between a pressure disk and the clamping part and are acted upon in an adjustable fashion via an adjusting nut by means of a spring force. The clamping part and the sleeve-shaped hub have an integral design.
GB 2321504 A describes a friction clutch with a first ring and two internal rings, which each have frustoconical coupling surfaces that engage in one another. The magnitude of the generated frictional force, which is exerted perpendicular to the coupling surfaces, is varied by means of an adjustment member.
However, the last-mentioned friction clutches known from the prior art have previously only been known in the field of heavy mechanical engineering. Thus, for example, the one in DE 103 15 808 A1 is used to drive chain wheels. Accordingly, the known friction clutches are generally comparatively heavy, composed of many parts and have a high installation space. Until now there has not been a demand to use such friction clutches in the field of medical technology, particularly in the field of analytic test instruments.